The present invention relates to a display driver for driving a display panel.
In recent years, PDPs realized as thin, large-screen, high definition display panels have been receiving attentions. The PDPs have a plurality of discharge cells arranged in a matrix as pixels and display images using emission caused by discharging of the discharge cells.
A common AC-type PDP has a plurality of display electrodes arranged in parallel and a plurality of data electrodes arranged in lines perpendicular to the lines of display electrodes. A display driver which drives these data electrodes can be considered to drive capacitive loads.
Achievement of larger screen, higher definition and higher luminance in PDPs entails the necessity of more output signals and increase in voltage of the output signals in display drivers which drives the PDPs. Therefore, suppression of power consumption caused by driving the data electrodes and suppression of heat generation by the driving are particular requirements.
Application of different potentials to two data electrodes causes these electrodes to behave as one capacitor. In other words, a capacitive load occurs between the electrodes, and large power is consumed for driving this capacitive load. Known examples of a technique for reducing such power consumption are described below.
In a liquid crystal driver example where the voltage between opposite electrodes is constant and the driver carries out dot-inversion driving, a switch is provided between output terminals, and a short-circuit is established between the output terminals. As a result, the short-circuited output terminals have closer potential values, so that power consumption by the next display driving cycle can be reduced (see, for example, Japanese Laid-Open Patent Publication No. 9-212137 (FIG. 1)).
In another liquid crystal driver example which carries out line-inversion driving, all the output terminals are connected to a common signal line at an intermediate voltage which is substantially half of a drive output voltage (see, for example, Japanese Laid-Open Patent Publication No. 2001-255857 (FIG. 1)).
Still another liquid crystal driver example has common potential lines which maintain the voltage closer to the output voltage than the intermediate voltage, i.e., maintains higher and lower voltages than the intermediate voltage. Prior to driving, the output terminal is connected to any of the common potential lines according to the tendency of change in potential of the signal at the output terminal at the time of switching of the display line. As a result, the load is decreased, so that the power consumption can be reduced (see, for example, Japanese Laid-Open Patent Publication No. 2003-271105 (FIG. 1)).
The first-described liquid crystal driver example is predicated on the dot-inversion driving. This case is achieved by AC driving, such that potentials of the opposite polarities are necessarily applied to adjacent terminals. It has also been found that, for display of the next line, the output terminal infallibly changes to a potential of the opposite polarity. Thus, control of the switch between the terminals is not affected by pixel data to be displayed.
However, in the case of a data display driver for a PDP which outputs pixel data as they are, whether or not adjacent pixels have opposite polarities and whether or not adjacent lines of pixels have opposite polarities depend on pixel data. Since various pixel data of images have no regularity, the control scheme of the first example cannot be applied to this type of driver.
The second-described liquid crystal driver example requires that signals supplied to adjacent pixels have opposite polarities. Otherwise, power loss occurs when the driver operates. Further, it is necessary to provide an additional large capacitor, or the like, which is capable of supplying an intermediate potential.
The third-described liquid crystal driver example is predicated on a driving method where predetermined high and low voltages are alternately applied. Further, it is necessary to provide an additional power supply circuit which generates higher and lower voltages than the intermediate voltage and an additional large capacitor. Incorporation of these elements into a chip increases the chip area. Provision of these elements outside the chip increases the number of components.
In display drivers for PDP, potentials applied to adjacent pixels do not necessarily have opposite polarities. In many cases, pixel data are supplied to data electrodes as they are, or data electrodes are connected to common potential lines before they are driven as in the third liquid crystal driver.